CMOS (Complementary Metal Oxide Semiconductor) is an amplifying device for a voltage control, and is a basic unit for forming a CMOS digital integrated circuit. A CMOS circuit (a MOS integrated circuit formed by PMOS tube and NMOS tube complementary and commonly) may generate a low impedance path between a power source and a ground because of an interactive affection between parasitic PNP and NPN bipolar transistor. The low impedance path will generate a large current between the power source and the ground, which is called as a latch up effect.
In a liquid crystal display field, a thin-film transistor (TFT) provides a driving voltage through a voltage driving chip, the voltage driving chip includes a CMOS circuit. A power chip provides a control voltage and a driving voltage for the voltage driving chip. When the control voltage rises up before the driving voltage (that is, in timing, the control voltage is prior to the driving voltage), the CMOS circuit will not generate a latch up effect. When the control voltage rises up after the driving voltage (that is, in timing, the control voltage is late with respect to the driving voltage), the CMOS circuit in the voltage driving chip is easily to generate the latch up effect. When the latch up effect is generated in the CMOS circuit of the voltage driving chip, the MOS tube in the voltage driving chip will break. Therefore, in order to prevent the CMOS circuit of the voltage driving chip to generate the latch up effect, usually, a timing control circuit is added inside the power chip to control that the control voltage rises up before the driving voltage. However, after adding the timing control circuit in the power chip, if the timing control circuit is abnormal, the CMOS circuit in the voltage driving chip is easily to generate a latch up effect.